The geographical polarization of the American electorate: a country of increasing electoral landslides?

American politics have become increasingly polarized in recent decades, not only ideologically but also geographically. The extent of that geographical polarization is explored at the county and SMSA scales for the presidential elections held between 1992 and 2016 and also, at the much finer, precinct, scale for the 2008, 2012 and 2016 elections. The patterns that emerge show that much of non-metropolitan USA has becoming increasingly dominated by Republican party candidates, whereas the large metropolitan central cities remain dominated by the Democrats. Within those metropolitan areas, change, especially at the 2016 contest, was largely confined to their suburban districts.